Multiple Photoionization of C60

Relative C$_{60}^{2+}$/ C$_{60}^{+}$, C$_{60}^{3+}$/ C$_{60}^{+}$, and C$_{60}^{4+}$/ C$_{60}^{+}$ photoionization cross-section curves have been obtained using monochromatized light of the Synchrotron Radiation Center in the energy range between the double-ionization threshold (19 eV) and $K$-shell excitations (284 eV). In addition, we have measured the photoionization-induced fragmentation of C$_{60}$ for different charge states. Our measurements are a great improvement to existing data \footnote{T.\ Drewello {\it et al.}, Int. Journal of Mass Spectrom. and Ion Processes {\bf 124}, R1 (1993).} \footnote{A.\ Reink\"oster {\it et al.}, J.\ Phys.\ B {\bf 37}, 2135 (2004).} regarding energy range and accuracy. Of particular interest is the C$_{60}^{2+}$/ C$_{60}^{+}$ ratio curve that surprisingly exhibits a modulation with local enhancements of the ratio at certain excess energies (= photon energy minus double-ionization threshold). Our data analysis reveals that one of the two photoelectrons created in the double photoionization process has a de Broglie wavelength, calculated for each of the ratio-enhanced excess energies, that matches a certain distance in the C$_{60}$ cluster. These distances can be associated with the C$_{60}$ cluster's diameter, the diameter of a hexagon, and the distance between two neighboring carbon atoms \footnote{P.N.\ Juranic {\it et al.}, Phys.\ Rev.\ Lett.\ {\bf 96}, 023001 (2006).}.